1. Field of the Invention
The present invention relates to a thin-film magnetic head having at least an induction-type electromagnetic transducer, and a method of manufacturing the same, and to a thin-film magnetic head substructure used for manufacturing the thin-film magnetic head.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording density of hard disk drives. In particular, areal recording densities of latest hard disk drives have reached 80 to 100 GB/platter and are even exceeding that level. It is therefore required to improve the performance of thin-film magnetic heads.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording (write) head having an induction-type electromagnetic transducer for writing and a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, the write head incorporates: a medium facing surface (air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers. In the typical write head, the bottom pole layer and the top pole layer are magnetically coupled to each other via a coupling portion which is located away from the medium facing surface.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of the write head. To achieve this, it is required to implement the write head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other on a side of the medium facing surface, with the recording gap layer disposed in between, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve the write head having such a structure.
As the track width is decreased, it becomes harder to generate a high-density magnetic flux between the two magnetic pole portions that are opposed to each other with the recording gap layer in between. It is therefore desirable that the pole portions be made of a magnetic material having a higher saturation flux density.
When the frequency of the write signal is raised to increase the recording density, it is required for the write head that the speed of change of flux be improved, or in other words, the flux rise time be reduced. It is also required that degradation in the writing characteristics such as the overwrite property and the non-linear transition shift in a high frequency band be minimized. To improve recording characteristics in the high frequency band, it is preferable to reduce the magnetic path length. The magnetic path length is determined chiefly by the length of a portion of the bottom or top pole layer located between the coupling portion and the medium facing surface (referred to as a yoke length in the present application). A reduction in yoke length is effective in reducing the magnetic path length. To reduce the yoke length, it is effective to reduce the pitch of the turns of the thin-film coil, or the pitch of a portion of the turns which lies between the coupling portion and the medium facing surface, in particular.
As disclosed in the U.S. Pat. No. 6,043,959 and the U.S. Pat. No. 6,191,916B1, the thin-film coil of the thin-film magnetic heads is flat whorl-shaped and disposed around the coupling portion in many cases. In the thin-film magnetic head having such a structure, the thin-film coil generates many lines of flux in the neighborhood of the coupling portion. These lines of flux are introduced to the two pole portions by the top and bottom pole layers and used for writing.
In the thin-film magnetic head having the above-mentioned structure, however, it is impossible to effectively use the flux generated by the coil for writing. That is, it is known that only several percent of lines of flux generated by the coil is used for writing in such a thin-film magnetic head. In prior art the number of turns of the coil is increased to increase the lines of flux used for writing in this type of thin-film magnetic head.
A technique is disclosed in the U.S. Pat. No. 6,191,916B1 to dispose the turns of a second coil between the turns of a first coil for reducing the pitch of the turns of the thin-film coil.
In the U.S. Pat. No. 5,995,342, Published Unexamined Japanese Patent Application 2000-311311 and the U.S. Pat. No. 6,459,543B1, a thin-film magnetic head is disclosed, the head having a thin-film coil wound in a helical manner around at least one of the top and bottom pole layers. In this magnetic head a part of the thin-film coil is located between the coupling portion and the medium facing surface. The head having such a structure allows the lines of flux generated by the coil to be effectively utilized for writing. As a result, it is possible to make the number of turns of the coil smaller than that of a thin-film magnetic head having a flat whorl-shaped thin-film coil. A reduction in yoke length is thereby achieved.
As described above, it is desirable to reduce the yoke length of the thin-film magnetic head for improving the writing characteristics in the high frequency band. To achieve this, it is effective to reduce the pitch of a portion of the turns of the thin-film coil located between the coupling portion and the medium facing surface. On the other hand, it is desirable to increase the number of turns of the coil so as to improve the writing characteristics of the magnetic head.
In the case of either the thin-film magnetic head having the flat whorl-shaped coil or the thin-film magnetic head having the helical-shaped coil, to increase the number of turns of the coil and to reduce the yoke length at the same time, it is inevitable to reduce the width of the portion of the coil located between the coupling portion and the medium facing surface. However, a problem that the resistance of the coil increases thereby arises.
As the resistance of the thin-film coil increases, there arises a problem that the pole portions may protrude toward the recording medium due to the heat the thin-film coil generates so that the pole portions are likely to collide with the recording medium.
Therefore, in the conventional thin-film magnetic heads, to avoid the problem that may result from an increase in the resistance of the thin-film coil, it has been unfeasible to considerably reduce the yoke length.
The thin-film coil is typically formed through frame plating. The frame used for frame plating has walls each of which is disposed between adjacent turns of the coil. It is necessary that each of the walls be wide enough to maintain the shape of each of the walls. As a result, it is difficult to reduce the space between adjacent turns of the coil when the coil is formed through frame plating.
Through the use of the technique disclosed in the U.S. Pat. No. 6,191,916B1, it is possible to reduce the space between adjacent turns of the flat whorl-shaped thin-film coil. In the thin-film magnetic head disclosed in the U.S. Pat. No. 6,191,916B1, however, the flat whorl-shaped coil is used for generating lines of magnetic flux, and it is therefore impossible to effectively use the lines of flux generated by the coil for writing as described above.